slaved stepper problems

[Jonathan]

What stepper driver is it? 2.99V might not be enough? What's the equivalent voltage for one of the drivers that is working.

For instance, if it's a M752 driver they have a 270 ohm resistor in series with the opto-isolator, which gives the correct current for those to switch on with 5V, not 3V ... 3V may not be sufficient.

Just re-read your post and noticed you said all the drivers, so that's all irrelevant! I'll leave it just in case it helps someone else.

It doesn't sound like a mechanical fault, as the motor isn't stalling it's just moving the wrong way? Have you tried putting a different driver on the C-axis? Swap Y and C for instance...if it works then you know it's not a mechanical fault and must be something wrong with the driver. I once had an optoisolator break on one of my drivers, connected it wrong, so I just soldered a new one in and it's fine.

[johngoodrich]

actually just came in from doing it. the driver obviously has problems. they are 452 drivers, all of them. any ideas what could be wrong with it.

[Jonathan]

So just to be clear, the suspect driver works fine except for only going in one direction and the symptoms are the same if you feed it from the breakout board outputs that work with other drivers, and the motor/slaving works if you use a different driver for C?

Is the driver heating up abnormally?

Assuming the above is right, the driver is ignoring the direction input. That implies the opto-isolator inside is broken (so the PGA isn't getting the signal), or something else which will be more difficult to fix. If you want to post it to me I can have a look at it and hopefully fix it, just send me the return postage.

[johngoodrich]

just tring to get hold of bloke i bought them off to get replacement, refund seeing that they are less than 3 mnths ols. if not i will take you up on your offer. thanks a lot

[Gary]

actually just came in from doing it. the driver obviously has problems. they are 452 drivers, all of them. any ideas what could be wrong with it.

If the voltage going to the direction is only 2.99V, it is unlikely a problemn with the driver but the signal is too low for the opto to change.
What are you using to power the 5V on the breakout board?
If you are using USB, dont and get yourself a 5V power supply.

[Jonathan]

If the voltage going to the direction is only 2.99V, it is unlikely a problemn with the driver but the signal is too low for the opto to change.

3V is borderline, more susceptible to interference, (driver manual says minimum 7mA, 2.99V gets about 4-5mA) yes, but as the same signal works with the other drivers it's less likely to be that. Still it's worth just applying 5V and 0V to the direction pin from a power supply, or directly from the USB +5V to check.

[Jonathan]

I've now tested your driver. I connected it up in place of my Y-axis driver. I use *752 series drivers, so they're on 70 volts hence I used a lab PSU set to 48V for your driver. It works fine... I've not done anything to it, just connected it and changed the switches to 1600 step/rev as that's what I use. Then tested it on 800 and 400, not really expecting that to make a difference, and it didn't.

Interestingly the motor runs more quietly and possibly more smoothly (difficult to tell of course) with your driver. I'll have to test my own driver on 48V to see if it's just the lower voltage causing that. If not then that's useful information as it implies they use different control algorithms. As expected though the feedrate I can get with 48V is less (24000mm/min @ 2000mm/s/s acceleration) but still plenty!

So what would you like me to do now? Just send it back and hope it starts working on yours too? I'll have a look inside anyway just to be sure.